SUBCELLULAR-DISTRIBUTION OF XENOPUS XEL-1 PROTEIN, A MEMBER OF THE NEURON-SPECIFIC ELAV HU FAMILY, REVEALED BY EPITOPE TAGGING/

Drosophila and vertebrate elav/Hu genes are involved in the developmen t and the maintenance of the nervous system, They all encode proteins that contain three RNA recognition moths (RRM) and are thus expected t o play a role in RNA metabolism, Drosophila ELAV and RBP9 proteins wer e reported to be exclusively distributed in nuclei of neurons, whereas known human Hu proteins display a bipartite nuclear and cytoplasmic d istribution, We have previously isolated a member of this family in Xe nopus Xel-1, that is exclusively expressed in neural tissues from the early tailbud stage onward, In the present study, we report on the sub cellular distribution of XEL-1 protein using myc epitope tagging, a st rategy allowing the study of a single member of the ELAV/Elu family, W e show that the subcellular distribution of exogenous XEL-1 protein in neural tissues depends on developmental stages, In the neural tube at the neurula stage, where endogenous Xel-1 is not expressed, exogenous tagged XEL-1 protein is localized in both the nucleus and the cytopla sm, At the tailbud stage, where endogenous Xel-1 is expressed, exogeno us tagged XEL-1 protein is localized essentially in the cytoplasm of n eural tube cells, In contrast, exogenous Drosophila ELAV protein local izes to the nucleus at all stages in Xenopus embryos, The variability in the subcellular localization of ELAV/Hu proteins in different speci es may have functional implications.